C-alkyl derivatives of c2b5h7 and c2b4h8 and preparation thereof from dihydrocarboranes



ONAK 5 OF 0 3 mm) c 13 H. HEREOF FROM ARBOR 20, 1964 Jan. 7, 1969 C-ALKYL DERIVATIVE AND PREPARATION '1' DIHYDROC ANES Filed Aug United States Patent 3,420,889 C-ALKYL DERIVATIVES OF C2B5H7 AND C B H AND PREPARATION THEREOF FROM DIHY- DROCARBORANES Thomas P. Onak, Pasadena, Calif., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Aug. 20, 1964, Ser. No. 391,056 U.S. Cl. 260606.5 13 Claims Int. Cl. C07f /02 ABSTRACT OF THE DISCLOSURE The description discloses a process which produces a high yield of carboranes from dihydrocarboranes. Upon heating a C-alkyl derivative of dihydrocarborane a C-alkyl derivative can be obtained. A high yield is obtained when the heating process is accomplished in the presence of trimethylamine.

The present invention relates to a process which produces a high yield of carboranes from dihydrocarboranes. These carboranes may be used as highly stable fuels and also are an intermediate toward a high temperature rise polymer.

The carboranes sym-C B H unsym-C B H sym- C B H and C2B5H7 have been prepared from dihydrocarborane C B H in very low yields by the silent electric discharge process. While this process shows that carbo ranes can be produced from dihydrocarboranes the yield is not satisfactory for commercial utilization of the end products.

Upon seeking processes which would produce a higher yield it was thought that catalytic removal of H or removal of EH by a Lewis base might lead to the preparation of C-alkyl derivatives of C B H and C B H respectively. Since the loss of H and EH occurs in related boron hydrides merely by heating, a pyrolysis of dihydrocarboranes was expected to produce the carboranes C B H and C2B3H5.

Surprisingly, upon undertaking the pyrolysis, no alkyl derivatives of C B H were detected and C-alkyl derivatives of C B H were produced in an unanticipated abundance. Further, alkyl derivatives of sym-C B H were isolated with no alkyl derivatives of unsym-C B H being detected. Upon further search for high yield processes it was discovered that the presence of trimethylamine during the pyrolysis significantly increased the yield of sym- C B H The carbons in the structure of both of the carboranes produced were separated which provided these products with greater stability than the dihydrocarborane wherein the carbons are adjacent one another.

Accordingly, an object of the present invention is to provide a process which will produce a high yield of stable carboranes from dihydrocarboranes.

Another object is to provide a process which will produce a high yield of C-alkyl derivatives of C2B5H7 from C B H A further object is to provide a process which will produce a high yield of sym-C B H from C B H A still further object is to produce new C-alkyl derivatives of carborane 2,5 and carborane 2,4.

The above stated objects as well as other objects will become readily apparent by the following description.

FIGURE 1 represents the structure of a R C B H molecule;

FIG. 2 represents the structure of a R C B H molecule; and

FIG. 3 represents the structure of a sym-R C B H molecule.

3,420,889 Patented Jan. 7, 1969 "ice The present invention will be more readily understood from the following examples which illustrate several embodiments thereof. All temperatures are in degrees centigrade.

EXAMPLE I C,C-dimethyldihydrocarbcrane-2,4, hereinafter represented as Ia was first prepared. To 10 ml. of 2,6-lutidine were added 17 mmoles of pentaborane and 30 mmoles of Z-butyne. After stirring the mixture for 5 hours at room temperature the volatile components were vacuum fractionated through traps at and '-l90. To the contents in the -80 trap was added 25 ml. of freshly distilled boron trifluoride ethyl etherate. After stirring the resulting heterogeneous solution for 15 minutes at room temperature the volatiles were fractionated through 20-, 80, and l traps. Crude Ia which formed in the 80 trap was stored over 1 g. lithium aluminum hydride for 1 hour and then fractionated through traps at 70 and 190. The 70 trap contained 6.9 mmoles (04%) of la.

One mmole of la was obtained and then sealed in a 25 ml. flask equipped with a 5 mm. diameter tube for taking a nuclear magnetic resonance (N.M.R.) spectra. The lowest temperature at which the disappearance of dihydrocarborane occurred at a reasonable rate was 290". This was determined by following the H N.M.R. while increasing the temperature. The minimum temperature was applied for about 20 hours until 100% of the Ia was decomposed. The contents of the flask were then gas chromatographed.

The contents were found to be approximately 25% C,C-dimethylcarbmane-2,5, hereinafter referred to as IIa, approximately 5% of C,C-dimethyl-sym-carborane-2,4, hereinafter referred to as 111a and byproducts of alkanes, ethane, traces of boron hydrides and possible traces of propane and butane.

EXAMPLE II C-n-propyldihydrocarborane-2,4, hereinafter referred to as lb, was first prepared. This was accomplished in the same manner as described in Example I for preparing Ia except 30 mmoles of l-pentyne was employed in lieu of 2butyne. The yield of purified Ib was 6.5 mmoles (38%).

One mmole of lb was sealed in the 25 ml. flask and treated in the same manner as Ia was treated in Example I. The temperature was held at 300 for approximately 20' hours. The contents were approximately 30% C-n-propylcarborane-2,5, hereinafter referred to as IIb, approximate 2% C-n-propyl-sym-carborane-2,4, hereinafter referred to as III-b and byproducts such as alkanes, propane, n-butane, traces of boron hydrides and possible traces of ethane.

EXAMPLE III Ia was reacted in the flask in essentially the same manner as described 'for Example I except 1 mmole trimethylamine was added to the contents of the flask. The temperature was held at approximately 260 for 20 hours. Prior to the gas chromatography the trimethylamine was removed by fractionating through traps at 90 and Examination of the 190 bath indicated a nearly quantitative recovery of the trimethylamine originally present.

The results were approximately 15% 11a and approximately 25% IIIa, the trimethylamine being quantitatively recovered.

EXAMPLE IV One mmole of Ib was reacted in the flask in essentially the same manner as described in Example 11 except 1 mmole of trimethylamine was added to the contents of the flask. The temperature was held at approximately 280 for 6 hours. Prior to the gas chromatography the trimethylamine was removed through traps at 90 and -190. As in Example III examination of the l90 bath indicat d a nearly quantitative recovery of the trimethylamine originally present.

The resulting contents were approximately 15% 11b, approximately 20% IIIb, the trimethylamine being quantitatively recovered but contaminated with traces of boron hydride.

EXAMPLE V One mmole of la was reacted in the flask in essentially the same manner as described in Example I except 1 mmole of isobutane was added. The temperature was kept at approximately 280 for 6 hours. After the pyrolysis the reaction mixture was introduced immediately onto the gas chromatography column for separation.

The resulting contents were approximately 30% Ila and approximately Illa. The isobutane was quantitatively recovered.

Table I is a tabulation of the results obtained in the five examples given above.

TABLE I Dihy- Minimum Volatile products dro- Other pyrolysis (percent) Ex. earmaterial conditions bopresent ranes Temp., Hrs. Carbor- Sym-ear- C. ans-2,5 borane-2,4

None 290 20 Ha, 25 Illa, 5. o 300 20 Ilb, 30.-.. IlIb, 2. (TMA) 260 20 Ila, 15.-- IIIa, 25. (TMA). 280 6 III), 15 IIIb, 20. Isobutane. 280 35 Ha, 30 IIIa, 5.

Nomenclature: Ia-C,O-dirnetl1yldihydroearborane-ZA; Ib-C-n-pro pyldlhydrocarborane-2,4; Ila-C,C-dimethylearborane-Zfi; IIb-C-n' propylcarborane-2,5; Illa-C,C-dimethyl-sym-earbcrane-2,4; IIIbC' n-propyl-sym-earboraneZA; TMATrimethylarnme.

It is to be noted that when the pyrolysis is carried out in the presence of TMA the total quantity of carbons remains substantially unchanged but that the quantity of Illa and lIIb is greatly enhanced. When the pyrolysis is carried out in the presence of isobutane the same product distribution is obtained as when no diluent is used.

Several hypotheses appear plausible in explaining the change in distribution of the carboranes when the pyrolysis is carried out in the presence of TMA. One hypothesis is as follows:

if it is assumed that unsym-C B H once formed, does not rearrange at 300 to the symmetrical isomer then the following hypothesis is a possible explanation:

intramoleeular 1* (carbons separated) (slow step) The presence of TMA might catalyze the first two reactions in both hypotheses and yet not appreciably ailect the third reaction in each since the catalysis in the third reactions would involve a three-body collision.

The structures of the compounds were confirmed by B nuclear magnetic resonance (N.M.R.) tests. It was determined that Ia and lb structurally resemble a pentagonal pyramid, as shown in FIG. 1, that H21 and Ilb structurally resemble a trigonal bypyramid, as shown in FIG. 2, and that Illa and IIIb structurally resemble an octahedron, as shown in FIG 3. It is to be noted that the separation of the carbons in FIGS. 2 and 3 result in a more thermodynamically molecular species of the II and III series than where the carbons are adjacent one another.

The alkane side products produced during the pyrolysis rearrangement indicate that the skeletal carboncarbon bond is rather easily broken. It is to be noted that n-butaue is formed from the pyrolysis of lb, however, no pentane is found. Further, a considerable amount of propane is formed in addition to n-butane, and yet none of the parent (nonalkylated) carboranes are formed in the process. It is probable that the dihydrocarboranes and/or carborane radicals lead to these side products.

Table 2 below shows the physical data for the carboranes and the dihydrocarboranes, in the above examples:

TABLE 2.PHYSICAL DATA FOR THE CARBORANES AND DIHYDROCARBORANES Gas chrorna- Mass Spectrum; Melting Compound tography; Rv observed parent Point peak 1 Not taken. 2 Glass.

The melting points are in good relative agreement with the symmetry of the structures of the dihydrocarboranes- 2,4, sym-carborane-2,4 and carborane-2,5. The series Ia, Ila, 111a and the series lb, IIb, and IlIb represent a progression to greater symmetry and, therefore, one would expect the increase in the melting point. The a compounds containing methyl substitutes on each of the two skeletal carbons melt at a higher temperature than the b compounds with a propyl group on only one of the skeletal carbons.

It is now readily apparent that the present invention provides processes which produce a high yield of carboranes from dihydrocarboranes. By a pyrolysis of dihydrocarboranes a high yield of C-alkyl derivatives of C B H are produced and when the pyrolysis is carried on in the presence of TMA a high yield of sym-C B I-I is obtained. By a separation of the carbons in the structure the products will be more stable than the dihydrocarborane.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. C,C-dimethylcarborane-2,5, C B H 2. C-n-propy1oarbonane-2,5, C B H 3. C,C-dimethyl-sym-oarbopane-2,4, C B H 4. C-n-propyl-syrn-carborane-ZA, C B H 5. A process for preparing C-methyl derivatives of 4- boron carboranes and 5-boron carboranes comprising the steps of:

(a) heating a C-methyl derivative of a 4-boron dihydrocarbor'ane until the C-methyl derivatives of said carboranes are formed and (b) recovering said C-methyl derivatives of said carboranes.

6. A process as claimed in claim 5 wherein:

(a) said heating of the C-methyl derivative of said 4-boron dihydrooarborane is conducted in a temperature range of 250-300 degrees centigrade.

7. A process as claimed in claim 5 wherein:

said heating of the C-propyl derivative of said 4-boron dihydrocarbonane is conducted in a temperature range of 250-300 degrees centigrade.

8. A process for preparing C-methyl derivatives of carboranes comprising the steps of:

(a) reacting pentaborane with butyne in the presence of lutidine to obtain a C-methyl derivative of a 4- boron dihydrocarborane;

(b) heating the dihydrocarborane in the presence of tirmethylamine until the carboranes are formed; and

(c) recovering the carboranes thus formed.

9. A process for preparing C,C'-dimethycarbonane-2,5 and C,C'-dimethyl-sym-oarbonane-2,4 comprising the steps of:

(a) heating C,C'-dimethyldihydrooarbcrane-2,4 at a temperature between 250 C. and 300 C. until the 4-boron carboranes and 5-boron carboranes are formed and (b) recovering said carboranes thus formed.

10. A process as claimed in claim 9 including the step of:

(a) heating the C,C-dimethyldihydrocarborane-2,4 in

the presence of trimethyl'amine.

11. A process for preparing On-propyl-carborane-LS and C-n-propyl-sym-carborane-2,4 comprising the steps of (a) heating C-n-propyldihydrooarborane-2,4 at a temperature between 250 C. and 300 C. until 4-boron carboranes and 5-boron carboranes are formed and (b) recovering said carboranes thus formed.

6 12. A process as claimed in claim 11 including the step of:

(a) heating the C-n-propyldihydrooarborane-2,4 in the presence of trimethylamine. 13. A process for preparing C-propyl derivatives of 4- boron and 5-boron carboranes comprising the steps of heating a C-propyl derivative of a 4-b0ron dihydrocarborane until the C-propyl derivatives of said carboranes are formed; and recovering said C-propyl derivatives of said oarbonanes.

References Cited Robert E. Williams et al.: 140th, A.C.S. Meeting, Chicago, September 1961.

Thomas P. Onak et al.: J.A.C.S., vol. 84 (1962), pp. 2830-2831.

HELEN M. MCCARTHY, Primary Examiner.

W. F. W. BELLAMY, Assistant Examiner.

US. Cl. X.R. 4476; 2602 

